Transmitter-receiver



Feb- 14, 1961 R. v. WERNER ETAL 2,972,047

TRANSMITTERRECEIVER Filed Nov. 21, 1955 INVENTOR. @abe/* V. Wer/7er BYJames W. Crooks @Ober C`.WeV/

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TRANSMITTER-RECEIVER Robert V. Werner, San Diego, Robert C. Weaver, LaJolla, and James W. Crooks, Jr., San Diego, Calif., assignors to GeneralDynamics Corporation, San Diego, Calif., a corporation of Delaware FiledNov. 21, 195s, ser. No. 548,182

4 claims. (c1. 25o- 15) This invention relates to that class ofreceiver-trans?.

mitter combinations vknown as transponders, and more particularly, to atransponder wherein an electronic servo feedback system controls thecharacteristics of a modulated radio-frequency signal transmitted inresponse to a received modulated radio-frequency signal.

The form of transponders heretofore knownV to the art usually haveincluded a receiver and an independent transmitter. In such devices, thesignal output from a conventional receiver having a local oscillatorwith an associated frequency control device, an intermediate frequencyamplifier and a detector, is employed to modulate aconventionaltransmitter having the usual amplifiers, modulator, oscillator, andfrequency control equipment. Such transponders require precise frequencycontrol associated with both the receiver local oscillator -and thetransmitter. Frequently, transponders must. operate within precisefrequency 1imitations. Thus, bulky and complex frequency controlapparatus must be provided at both the receiver and transmitter.Furthermore, it'is frequently necessary in such transponders for thetransmitted modulation to maintain a constant phase and frequencyrelationship to the received modulation. Faithful retransmission of areceived signal, both in phase and frequency, requires precise controlof local oscillator frequency in order to maintain the differencebetween the received carrier frequency and the local oscillatorfrequency precisely at the center frequency of the intermediatefrequency, amplifier. As is well-known to .those skilled in the art,distortion of the phase and frequency relationships of the modulatingsignal result if the intermediate frequency is not maintained preciselyat the frequency to which the IF amplifier is tuned. In order tomaintain such a precise relationship between the received signalfrequency and the frequency of the local oscillator, complex automaticfrequency control systems must be provided. l Another form oftransponder heretofore known to the art merely consists of a high gainradio-frequency amplifier with the input terminals connected to areceiving antenna, and the output terminals thereof connected to atransmitting antenna. Although such transponders are satisfactory at lowfrequencies, radio-frequency ampli- 2,972,047 Patented vFell. 14, -1961modulating signal. The feedback circuit additionally serves to maintainthe phase and frequency characteristics of the transmitted modulatingsignal as a faithful reproduction of the received signal.

It is therefore, an object of this invention to provide a transpondercapable of receiving and retransmitting a modulated signal.

bears a xed frequency relationship to the received radio-= frequencysignal.

Another object of this invention is to provide a transponder wherein thetransmitting oscillator also serves as a local oscillator atthereceiver.

Another object of this invention is to provide a trans?v ponder whereinthe modulation of -a transmitted signal is 1 determined by themodulation of a received signal.

Another object of this invention is to provide means enabling thefrequency and phase relationships of al transmitted modulating signal tobe controlled by a received modulating signal through a feedback loop.

Another object of this invention is to provide a transponder with afeedback circuit capable of compensating for the nonlinear response tothe modulating signal of various portions of the transponder. Anotherobject of this invention is to provide a trans-I ponder capable offaithfully transmitting a modulated microwave signal at a fixedfrequency difference in ref` lation to a received modulated microwavesignal.

Another object of this invention is to provide a micro--v wavetransponder which faithfully retransmits a received "f modulationaccurately imposed upon a precise carrier;

ceive and transmit microwave signals, is connected to a ication becomesincreasingly diflcult at higher frequencies, particularly when a broadband of frequency modu; latedsignals must be amplified. In particular,such transponders are impractical at microwave frequencies.

A transponder constructed in accordance with this invention may includea receiver, a radio-frequency oscillator, and a feedback circuit. Meansare provided whereby the radio-frequency oscillator simultaneouslyserves as a local oscillator in conjunction with the re? ceiver, and asa transmitting oscillator. ,By means of the feedback circuit, thefrequency of the radio-frequency oscillator is maintained vat afrequency differing from that of the received signal by an amount equalto the receiver intermediate frequency. Furthermore, theifeedbackcirguit serves tomodulate the oscillator with the received waveguide Yjunction 12. A. first arm 13 of Y junction 12 is connected to amicrowave filter 14, tuned to pass the frequency of the received signal.Such microwave filters are well-known to the art, and may comprise aresonant cavity, a plurality of iris diaphragms or other suitablearrangements. The signal passed by filter 14 is applied to a crystalmixer 15, of a type well-known to the art. The Y junction 12 isfurnished with a second arm 16 connected to a second microwave filter17. Filter 17, which may be similar in structure to filter 14, is tunedto pass the transmitted radio-frequency signal. A suitableradio-frequency oscillator 21 generates the transmitted radio-frequency,and, additionally, provides the local oscillator signal to crystal mixer15. Radio-frequency cable 22 connects the output of radio-frequencyoscillator'21 to filter 17.

A small portion of the transmitted radio-frequency signal generated byoscillator 21` is allowed to leak through arm 13 of Y junction 12 andthrough filter 1'4 to crystal mixer 15, thereby furnishing a localoscillator signal to crystal mixer 15. A semi-conductor crystal d iode23, of a type well-known to those skilled in the art, is provided inmixer 15 to generate a beat frequency at the intermediate frequency ofthe receiver. Exemplarily, a received radio-frequency signal of 5060mega.y cycles may be applied to mixer 15, and beat with the transmittedradio-frequency signal of 5000 megacycles from microwave oscillator 21.A resultant intermediate frequency signal o f 60 megacycles is,therefore, furnished. to'intermediate frequency amplifier 24` by crystalmixer 1'5. 'Pheintermediate frequency s-ignalA isy amplied byyintermediate frequency ampliiier 24, and is applied to discriminatordetector 25 wherein the modulating signal imposed upon; the intermediatefrequency sifgnaliA is detected. AlthoughY a frequency modulation-ldiscrir'n'tifnator isy disclosed l'eein'lin connection witha'ffrequency' modulated signal, it will be apparent'that an amplitudemodulationl detector may b eemployed ini place'- thereof for-use; in'connection". with anV amplitude4 modulated! signal. y I A As iswell-knownz'to those slcillecll in thefwart, the modulating signals'detected by' al dis'cri'rninat'or maybe alband" of frequencies rangingfrom direct current through? as high a frequency as may be desired:EXe'mplarily, in= the herein dsclose'cl-eijlodin-ht' of thisiri'Vel-'t'tiofnA themodulating signals-may includeabandaof-Jfr'equencies' ranging, from O to .1 kilocycles-pe'r-second=. yA

The =rnutrlnatilig signals' detetect-V by disrirrfi.Batory 2S ar'e'lapplied by rnzrisoftconductors 26 and 27 to aDC'.v amplifier'incorporating ccnnpensating impedance. network'. The discriminatori'output signal, -present'- on conductors 26' and 27,' is'applied to alfirstl group of com' pensatig `impedaln'ces in cluc'lng al resistor 31in series with conductor 26,A a capacitor 3'2 and resistor 33 in seriesWithconductor 26, and a capacitor 32 and resistor 33 in serial relationto one another, connected betweeriref, s'istor 31- a'rid conductor 27.Compensating resistor 31 and capacitor 32 are connected'to' controlelect-rode 340i electron discharge" device 35; Inf addition tofco'ntr'ol-electrode'34, electrondischar'ge'dev'ice 35 includes acathode 36; andaric'idY 37; screen. electrode 41, andy suppressor electrodJiZ,lCathode-l-islconnected-tov conductor 27 through-a' resistor 43. Inaddition, cathode 36 yis connected to suppressor electrode 42.` Anode.37 is con` nectedl to' a-jsecor1d compensating' network including, acapacitor46 and an inductance- 47 connected fin paralleli Bothofsaidparallel circuits'4 are serially coniiect'ed'to one another, and toanode 37 of electron discharge device 35. Ariod'e 37 is connected toterminal 51 of power supply 542 By'meansf 'of conductor 53, inductance47-V and resistor 45. Cathodeof discharge device35. is c'orinected'toterminalS- of powersupply 52 throughconductor `27 and-resistor 43. Anegative potential of 1200 volts, provided' at terminal 53, is appliedVto catho'de; Terminal 51 of power supply52 provdesi a negative 15otential' of 60'() voltstov anode 37 .of discharge device 35: by means ofconductory 53. supply 52-is grounded,v It willbe apparent, therefore,thatfan'ode 37 yis supplied wi'thva potential which is600 volts morepositive'than 'the potential; of cathode34t `In addition, 'screenelectrode 141 ris connectedgto conductor The third terminal v54`of1povve'r 4, 56 mayfvary-thevoltage-across oscillator- 21 in--responseto a signal applied to control electrode in a manner more fullydisclosed hereinbelow.

Oscillator 21 includes a collector electrode `67, connected to ground, acontrol gridr 71 connected to anode 61 of discharge device 56",'alrstCo'avity 72, a second cavity 73, and a third cavity 74. Cavities-72, 73 and 74 are tuned to the desired frequency, eXemplanily, 5000megacycles.- Anv oscillator Ais formed'by cavities 721a1'1div 73;vconnectedYV by a feedbackl radio-frequency' line 75. Cavity 74 isemployed as a tuned buffer amplifier. As? is well-known to thoseskilled-irl'thev art, such= a thre'e'cavity velocity modulated electrondischargejdevice functions as an oscillator with anvassonciated bufferamplifier. The output signal from'cavity'l-74 is-col'lpledt to lter 17by means of radio-frequency cable 22.

In the herein disclosed embodiment of this invention,

yitisassum'ed .that afrequency modulated radio-frequency carrier isreceived by antenna means 11.. The radiofrequencyV carrier, eXemp'larilyatl a frequency. of: 5060 megacycles per second, passes through arm 13of.Y junctionv 1.2, through 'tunedilter 14, and'is applied tocrystalmixer 15. quency ofoscillator 21, exemplarily 5000 megacycles persecond, a high impedance is presented by arm 16' of Y junction412',thereby'directin'g thereceived signal into arm13;v The SOOOme'gacycleper second signal generated by oscillator 21 is passed through tunediilterr V17, arm 16,r of Y junctionf-12; and is radiated by antennameans 11.v Filter 1.7 also serves to attenuate any noise which-may begenerated by oscillator 21:. AHowe-ver, lter 14.;is tuned broadly enoughto Aallow `asmall por'- tiopn of the 5000 megacycle signal to passthrough filterI 14an1l applied to crystal mixer 15. The received 5060megacycle, signal is ybeatagainst the 5000 megac'ycle s ignjalfrornoscillator 21:by m`eans of crystal diode2f3-in a; manner well-knowntolthose skilledy in the art,` andthe differencet frequency ofmegacyclesgenerated thereby'. is applied itointermediatefrequencyvamplier 24., Interi mediate frequency amplifier 24 may be ofany suitable type having a band widthbroad enough topass the range of`modulating signals.

vThe modulatedsignal amplifiedv by intermediate frequency amplifier 24is app-liedjto discriminator 25. As is well-known to those skilled inthe art, the output voltage of a. discriminator circuit is proportionalto vfre quency deviation.V Therefore, the modulating. signal isf removedfrom the v, frequency modulated intermedi- 53, therebyv maintainingscreen 'electrode 41 atthe "same potential as anod' 37.i

y The cmpesatedoutput 'signal 'from the anodeV 37V of electron discharge"device3`5.- is applied to controly elec# trode 55 `of eie'ctrondischarge 'device 5.6. Electro'lfdi'scharge 'device 56incl'udes a.cathode 57v and 'anfanode 61 in addition to control-'electrode 55.Electronl discharge deviceS' may additionally include a screen electrode62 andy a suppressor electrodeV 63: Cathode 57 is connected Atovterminalv 53 ofpower supply 52 .bymeasff'condetor frequency sigaar may15g;,'gener atedv byfv'el electron dischargedevive, 'such :as `discatefrequencycarrier by the discriminator and'is'furnishcd to acompensating circuit by means of-conductors 26 and 27; The modulating4signal appliedto `'conductors 26.y and 27Y by discriminator 25 may rangein frequency from direct current to several hundred kilocy'cles persecond. The phase and amplitude relationships of the broadr band offrequencies comprising the modulating signal may distorted by the phaseand gain characterf istics 'of the variouselements of the transponder. Acompensating circuitl comprising discharge Ivdevice 3S anditsaSSOci'ated impedance network is supplied -to'eorreot'suh distortionsLin a-r'nanner well-known to those skilled lin ther Suchcompensating,ne'twcrksl-- 'may be typ'efklisclosed on'y'pages l2444249 off RadioEngineersjHandbook,--'FirstEdition,by Termen, published by McGraw-HillBook Company. The compensated'- 'odixlatig signal'jis thenapplied 'to afreguencyl i dulator including modulator discharge device 56g Microwave:oscillator 21 "is frequency modulatedby dieha ye ,device5'6fin*'accordncejwiththe detected Inasmuchj aslter 17 is -tuned'topassthe 'fre.

feedback circuit composed of the mixer, intermediate amplifier,discriminator compensating amplifier, modu-i lator and oscillator. Thecompensated feedback loop thus established enables the wave-shape of thetransmitted modulating signal to be a substantially exact replica of thewaveshape of the received modulation. However, as is well-known to thoseskilled in the art, the various components of the transponder includedin such a feedback loop may each have individual transfercharacteristics which may distort the modulating signal. Therefore, acompensating circuit is provided for the purpose of equalizing the gainand phase relationships throughout the feedback loop. The compensatingcir c uit includes electron discharge device 3S, and a compensatingimpedance network including resistors 31, 33 and 45, capacitors 32, 44and 46, and inductance 47.I Re-` Sistors 31 and 33, and capacitor 32increase the gain., ofthe compensating circuit, and, therefore, of thefeed-4 back loop at low modulating frequencies, while ca,- pacitors 44and 46, resistor 45 and inductance 47 serve to increase gain atrelatively high .modulating frequencies: Therefore, the characteristicsof the compensating ciry cuit are such that the combined 'non-linearcharacteristicsof the various components of the feedback loop arecompensated for lby the complementary non-linear characteristics of thecompensating circuit. The resultant gain and phase characteristics ofthe complete modulatingI signal feedback loop are such that thetransmitted modu lating signal is a substantially exact, amplified,replica of the received modulating signal. The compensated modulatingsignal is obtained from' anode 37 of electron discharge device 35 and isappliedl -to control electrode 55 of modulator electron discharge device56. Cathode 57 of electron discharge device 56 is connected throughcathode bias resistor 64 to terminal Sitof power supply 52. As disclosedhereinabove, terminal 53 supplies a high negative potential, exemplarily1200 volts. Anode 61 of electron discharge device 56 is connected tocathode 65 of oscillator 21 through cathode bias resistor 66. Anode 67of oscillator 21, and terminal 54 of power supply 52 are both connectedto ground. It will be seen, therefore, that discharge device 56 andoscillator 21 are connected in series with the -1200 volts furnished bypower supply 52.y The compensated modulating signal applied to controlelectrode 55 of discharge device 56 varies the space current Howingthrough discharge device 56. Since oscillator 21 is serially connectedbetween power supply 52 and discharge device 56, the voltage acrossoscillator 21 is varied in accordance with the modulating signal.

The frequency generated by a velocity modulated electron dischargedevice, such as oscillator 2 1, is determined partially by the physicaldimensions of cavities 72, 73 and 74, and partially by the potentialapplied between cathode 65 and collector 67. The dimensions of cavities72, 73 and 74 serve to define a band of frequencies over whichoscillator .21- may operate. The particularfrequency within the -bandthus defined at which oscillator 21 operates -is` determined by thepotential present between cathodej65 5 vand collector i, 67. Asdisclosed. hereinabove, oscillator. 21 is connectedto ,-1200 voltterminal'53` of power 'supply'52 in series lrelation with modulatorelectron discharge device 56. The -normal current through the seriescircuit thus established is adjusted by means of discharge device 56 toestablish the des-ired voltage drop across oscillator 21, therebyestablishing the potential required for operation at the desiredfrequency. The compensated output signal from the compensating circuitincluding electron discharge device 35 is applied to control electrode55 of modulating electron discharge device 56. As is well-known to thoseskilled in the art, the signal voltage applied to control electrode 55varies the voltage drop across disagree? charge` device 56. Since aconstant potential of -1200 volts is present across the series circuitincluding modu-` lator device 56 and oscillator 21, if the voltage dropthrough modulator electron discharge device 56 is increased, the voltagedrop across oscillator 21 wil-l decrease, and vice versa, therebyfrequency modulating the output signal from oscillator 21. The frequencymodulated output signal from oscillator 21 is then applied to antenna 11through arm 16 of Y junction 12.

As disclosed hereinabove, the center frequency generated by oscillator21 is maintained at a value 60 megacycles per second from the centerfrequency of the received signal. The signal generated by oscillator 21is maintained at the requiredfrequency by means of. :themodulatingsignal feedback loop disclosed herein-A above, which also serves as anautomatic frequency con-l trol circuit. If the :signal generated byoscillator drifts from vthe required center frequency, a D.C. voltageof*A a polarity and magnitude proportional to the directionv v andamount of frequency drift is produced by discriminator 25.` The D.C.voltage thus generated is passed Ithrough the compensating circuit andis applied to modu lator electron discharge device 56. YThe modulatorvaries the voltage applied to oscillator 21 in the manner ds; closedhereinabove, thereby `returning the frequency of oscillator 21 to thecorrect value.

Although the embodiment of this invention disclosed hereinabove isadapted to transmit and receive signals inv the same direction over thesame antenna, it will be ap;

- parent that the transponder disclosed herein may be con# structed in amanner enabling reception of Va signal from one direction andtransmission in another direction. In such modifications, independentreceiving and transmibk tingy antennas are employed. The receiving`antenna may be connected directly to mixer 15, and a transmitting 'auftenna maybe connected to the buffer cavity 74 of oscila lator 21throughradio-frequency -cable 22. A small portion of the transmittedsignal generated by oscillator .21- may be applied to mixer 15 in anysuitable manner, exemplarily, by means of a coaxial line and a probecoupled to the mixer cavity.

It will be apparent, therefore, that hereinabove ,has been disclosed anovel transponder containing a closed loop feedback circuit for themodulating signal, and wherein a modulated 4signal received at onefrequency is transmitted at another frequency determined by the receivedfrequency. The received frequency modulated carrier is applied to acrystal mixer wherein it is beat with a small portion of the transmittedsignal. The difference frequency is amplified by an intermediatefrequency amplif fier and detected by a discriminator. The detectedmodulating signal is passed through a compensating circuit containing animpedance network wherein the phase and gain characteristics of thefeedback loop elements are compensated by the characteristics of thecompensating circuit. The compensated modulating signal is employed tofrequency modulate the transmitting oscillator. A small portion of themodulated output of the transmitting oscillator is fed back to themixer, thereby completing the feedback loop.

v While certain preferredA embodiments of the invention have beenspecifically disclosed, it is understood that the invention-- is l-notlimited thereto as many variationswill be readily apparent to `thoseskilled in the artn andthe invention is to be given its broadestpossible interpretation within the terms of the following claims.

What we claim is:

1. A transponder adapted to receive a signal at a first frequency andtransmit a signal at a second frequency comprising a receiver includingwave receiving means, a mixer, an intermediate frequency amplifier and adiscriminator for generating modulating signals in accordance with thereceived signal, a compensating circuit associated with said receivercomprising a first electron discharge device having a control electrodeand a cathode connected to saidV discrimnator, an anode, afrequency,

responsiveimpedance network connectedfto said anode,V

said impedance network including av first parallcllcircxiitv including acapacitor and -a resistor and Iascc'ond parallel,

circuit including a capacitor and an inductancc. in serial relationshipwith said rst Vparallelcircuit,whereby an equalized signal is produced-a`t said ',anodle, rvan .oscillator comprising a velocity modulated'electrondischarge-"dc-I vice forgeneratilig4 said second,'frclqte'nc'ysigiial,}means for frequency modulating said 4oscilla kr` inaccofileV with the equalized modulating lsignalscomprising a secondelectron discharge device'havingja control electrodejcqn;

nected to the anode of said ,firstelectron'discharge 'device and ananode in serieshwith said oscillator, 'nreans,l

for applying a portion of said secondfrequency signal tosaid mixer toproduce an intermediateirequency, and;

wave transmitting meansrassociated with j'said oscillator.` 2'. Atransponder adapted toreceive a, signal vat a first frequency andtransmit a signal at-'a Vsecond"'frequertcycomprising an antenna,a'firstfilterj` tunedtosaidfr'st' frequency, receiving means including,a mixer, an, intermediatefrequency amplierfa'nd a-dscriminator forgenerating modulating signals in accordance with thereceived` latingsignals, an, oscillator forsaid second# frequency-- signal, amodulatorcomprising anelectronfdischarge device'responsive tov saidcompensatingicir'cuitdn series l'relationshipl with said'oscillatorformodulatinglsaidfoscillator in accordance withl thecorrectedfmodulatinggsig'nals,--a f lter tunedl to saidsecondfrequency,meansforfapply# ing a tirst portion ofsaidsecondifreqn'ency signalto said mixer to produceanintermcdiatefrequency andf'a-s'e'c'ond pox-'tion tosaid antenna fortransmission;said`means-ncluding Va second lter tuned tosaidsecond'ifrequency, a. transmission line '.Y junctionl havingV a first:yterminal con` nected to said rst lter, asecond terminalconnectedf'tosaid'second filter, and a third terminal connectedto said antenna.

3. A transponder adapted to receive@alfrequencymodulated signal at a.first frequency and'tra'ns'mit-a. frequency modulated signal at asecondfrequency comprising; an antenna, a transmission line Yjunctionhavingt-afrst terminal connected to said antenna,arstrfi-lterltunedto pass-said rst'frequency connectedtoa-seco'ndztermnal ofl saidv Y junction, a receiver connected tosaid2rst=lter including `a mixer, an intermediate..frequency'iarnpliiier tuned to thedifference between saidfirstffrequencyfand said second frequency, and a discriminatoryfor.`recovering modulating signals, a compensating circuit' responsive Vtosaid discriminatorincludingan electron 'discharge device and anelectrical impedance network 4irl-'circuitwith said electron dischargedevice for correcting vdistortions f saidmodulating signals,-amulti-cavit y'velocityfmodulated oscillator for generatingsaidsecondfrequency-1signal,v a modulator comprising an electronvdischarge device having-a control electrode 'connected tosaidcompensating circuit and -an anode connected in serieswith said-oscill later for varying the! voltage across-said oscilltoi-,4-there7by varying the frequency vof saiclffsecondfrequencysignal in' accordancewith-saidporrected-modulating signals-,land

a second lter tuned'to pass'sa'id second *said discriminatordncludingl-`an' electron-discharge device` f 'aardbei nected between, saidoscillator and a tcrlliinalv said. transmSSionlineSY network wherebyaflargcfporf.

tion@ of said secondi frequency signal is. radiated by antennal and asmall portiojn oli` second,frequency` signal Passes Said. ir's't glter,beats. with 'Said.. ,rst tre: qnency sicnarins'aiidmixer. andgenerating; aniimermediats; fr equencyjsisnall.

4.` Atransponder adaptedtcxreceivea frequency'modnlated"'signal at aiirst 'frequency andtransmit a frequency modulated signal` at a secondfrequency comprising an antenna, a transmission line Yjunctionhaving-*a'iirstte'ia'nifu nal connected lto 'said antenna, a*firstltentunedj to `pass saisrsttfrequencyconnectedto afsecondterrninal-ofsaid Y-junction;;a receiver connectedjto saidfirstffilter including a mixer, an intermediateffrequency amplifiertuned-- to the difference between:taidhV first frequency-vandsaid"second frequency-,- andu 1a, discriminatoria-ifo! 'recoveringmodul-ating signals, afc'ompensatingciruitfresponsive 'to'I having-2acontrolf electrodeanano'clel andia cathode,- alirst impedance# networlei'nclucl'ing'va` first resistor connecting'v said controlelectrodeto-said discriminator and/'a secondresistonl and a 'capacitorlinA seriesJ-'between said Gc'ontrol electrode.' and 2 said cathodei a;second; impedance inetwrnfk:v

connected to saidranode comprising fa. rstfparallel circuit including.-atrsttcapaciton and aalresistor andfaisecond parallel'circuit ineserieswith-said=iirst parallel circutin-v cluding a second capacitor-'andaninductauce,y said .com-o, pensating circuit tltetebyfv correcting.distortions: ofv said modulating; 'signals,l; .at multi-@cavityvelocityvmodulated oscillator for generatingsaidsecondf--fleqllmyfsignaL a:modulatertcomprisinsfan .electrolldischarsedevice having a t control;electrorle1con,rlefctcclffto;said;-omptmsatinsu Cir:-

Cuitandtanfanode connected-'infseriestwith-saidossillawr:

` -for varying'the,AA voltageacross said-A'oscillator,

varying-the frequency-,Qi-Saidsecond-tfrequensy-Sisnalzia accordancewithsaid corrected modulating signa1sand e seeondoiilter tuned to pass` saidsecond frequencytcnff nected betweensaidoscillatorand a. third yterminal jof said transmission line Y network whereby ,amlargclporf tionof said second frequency signal is radiated byy saidl antenna and asmallportion of said second frequency signal passes said first filter, beatswith saidrst frequency, signal in, said mixer-and ,generatingy anintenmediatefre quncysigrlaL ReferencesCited in the le of #this patentUNITED 4STATES PATENTS pazza-.249; Y

